Clutch A comprises in particular:                A drive shaft E on which the individual components of the rotating clutch A are supported.        A bell F, which is firmly linked to the drive shaft E and the engine C and which also constitutes the support for the control piston L.        A disk carrier pinion H opposite the drive shaft E and freely rotating on bearings for transmission of the motion of the propeller axle D.        Clutch disks A1, whose rotational movement is guided by the bell F.        Driven clutch disks A2 arranged alternately with disks A1 and constituting the clutch package.        The control piston L (ring with hydraulic sealing on outer diameter to establish sealing towards the cylinder and hydraulic sealing on inner diameter to establish sealing towards the drive shaft), which is arranged opposite the counter disk 1, which cancels the assembly clearance between disks A1 and the counter disks A2 as soon as it starts moving through the agency of the hydraulic oil.        A return spring G (spring(s) capable of restoring the assembly clearance between the disks and counter disks), which makes sure that the piston L returns into the cylinder if hydraulic pressure is not available.        
If disks A1 and counter disks A2 are pressed against the spring-cushioned counter disk 1, then piston L will put the disk carrier pinion H, which is linked to the propeller axle D, in a rotational motion synchronous with that of the bell F, which is linked to the engine axle C, and will thus neutralize the relative rotation between disks A1 and the counter disks A2, a condition which is typical for “idling” (propeller axle D is disconnected from the engine axle).
The assembly clearance, which is equivalent to the distance covered by the piston L between its end positions, is referred to as “approximation distance” and determines (together with the area of the rim of piston L) the “approximation displacement”. The time needed to cover the approximation distance is referred to as approximation time.
Such a clutch can adopt two conditions:
a) Open: Piston L is pressed to its stop by the return spring(s) G (pos. 1 in FIG. 2) in bell F. The distance between disks A1 and counter disks A2 (assembly clearance) and the presence of lubricating oil permit their rotation relative to each other without influencing each other (in this condition, the engine axle C can rotate while the propeller axle D is stationary, and vice versa).b) Closed: Piston L is pressed against the clutch package by the hydraulic fluid (pos. 2 in FIG. 2). The distance between disks A1 and counter disks A2 (assembly clearance) is fully canceled. The presence of abrasion particles between disks A1 and counter disks A2, which are pressed together by the pressure effected by the piston L, which is proportional to the control pressure, causes their firm coupling and thus allows the flow of power between engine axle C and propeller axle D (in this condition, the propeller axle D can only run concurrent with the engine axle C, provided that sufficient thrust is generated by the control pressure).
According to the present state of the art—with particular reference to FIG. 3 of attached sketches—a hydraulic system for a marine reversing gear that does not feature electronic test equipment comprises a pump M to deliver hydraulic fluid from a reservoir N to the control pistons L1 and L2, i.e. one piston for each clutch (forward and reverse gear), two shuttle-type solenoid valves O and P arranged between pump M and piston L1 or piston L2, with one of them taking care of forward drive or discharge to the reservoir N and the other one taking care of reversing or discharge to the reservoir N, a bistable valve Q arranged in between the solenoid valves O and P and piston L, a control valve R arranged on the pressure side of pump M towards the discharge line to the reservoir N and provided with an adjusting device S, whose spring element T is linked to the bistable valve Q.
For smooth, jerk-free initiation of power transmission between engine C and propeller axle D, the above described device—at the end of the approximation distance (cf. functional diagram of FIG. 4 showing pressure in relation to time)—slowly and continuously elevates the pressure to a maximum level, starting from a level slightly above the max. level required for displacement of the piston L against the spring G.
The approximation phase starts at point 1 of the diagram; it ends at point 2.
The ability to transmit clutch power is proportional to the pressure supply of the pressure chamber, i.e. the volume available between bell F, drive shaft E and piston L.
This pressure also determines actuation times. If during the approximation phase a pressure level equivalent to that of the return spring G is reached, this will cause the piston L to remain in a state of equilibrium—its approximation speed will therefore be 0 while its approximation time becomes infinite. On the other hand, if pressure reaches a “very high” level, the actuation time can drop to a minimum value.
Hobby skippers generally believe that the response time of a boat to course change commands should be reduced as much as possible. The ideal response time would be 0.
The clutch contributes to the response time, but it is not the only component on which response time depends. Ergonomics of control and the integrity of the engine/propeller drive train prohibit influencing ramp time and force us to influence the approximation time. A number of solutions are available for this: Optimization/enlargement of the cross-section of lines leading from the pump M to the clutch; use of a different oil grade with different physical properties; modification of the delivery volume during the approximation phase; modification of the “displacement” of the clutch (either by reducing the cross-section of the piston in favor of a proportional increase in operating pressure or by reducing the assembly clearance of the clutch package); splitting of clutch “displacement” into two sections (a first one with a smaller cross-section for a faster acceleration phase and a second one with a cross-section equivalent to the rated cross-section); elevation of the minimum pressure level (in a traditional actuation system this reduces approximation time but increases the likelihood for jerks within the drive train during the actuation phase); use of the ECU together with the proportional solenoid vales O and P.
All these solutions—which can also be combined—have their limitations, due to the high expenses involved, but also because of the fact that they require the application of use specific solutions and the resulting difficulties involved in precise, detailed adjustment.